Conventional optical input power measurement solutions for optical data networks consist of average current-to-voltage conversion performed by a trans-impedance amplifier (TIA) or limiting amplifier (LimAmp). The TIA or LimAmp is provided in a receive data path of the optical data network. In the case of a Passive Optical network (PON), a primary function of use of one of these devices in an Optical Line Termination (OLT) application is to convert high-frequency photodiode current to digital voltage levels for data recovery. In some cases the TIA or LimAmp also provides an output voltage proportional to average optical input power, which is used by an external circuit to generate a Received Signal Strength Indication (RSSI) measurement.
Known optical network technologies such as BPON (i.e., Broadband Passive Optical Network) and GPON (i.e., Gigabit Passive Optical Network) use burst-mode transmission at relatively high bit rates. Accordingly, BPON and GPON are referred to herein as burst-mode enabled PON technologies. Facilitating input power measurement for burst-mode enabled PON technologies requires implementing functionality in a network's Media Access Controller (MAC) to coordinate Optical Network Unit (ONU) burst with the RSSI measurement. However, to date, no solutions for MAC-layer functions required for facilitating such conventional optical input power measurements are known to exist. One example of such MAC-layer functionality is facilitating control of an Analog-to-Digital Converter (ADC) for converting analog signalling information to corresponding digital signalling information.
Without imposing significant added cost and complexity, conventional optical input power measurement solutions will exhibit one or more limitations when implemented in relatively high bit rate applications such as GPON. One limitation is the response time for facilitating such measurements when using conventional optical input power measurement solutions. It is typically in excess of 1 millisecond. In a burst-mode system such as a GPON, where a timeslot on the shared medium (typically microseconds) must be allocated for the measurement, the time taken to measure power from one ONU affects the ability of the system to meet quality-of-service requirements for other end users. Accordingly, in a GPON system, a response time on the order of milliseconds is considered unacceptable. Another limitation is the dynamic range associated with such measurements. It is limited by the use of a voltage output that varies linearly with average photodiode current, which results in voltage output on the order of volts at the high end of the input power range and millivolts at the low end of the input power range. In the case where this output voltage is referenced to ground potential, great care is required in the circuit implementation to overcome effects such as noise and offset voltages. An ADC utilized in facilitating measure of the input voltage is required to have relatively high resolution in order to meet the accuracy requirement at low power levels. This resolution requirement contributes to increased cost as well as longer conversion time. Additionally, TIA transimpedance, which determines the current-to-voltage gain and therefore affects accuracy, tends to vary significantly over temperature and device lot. Still another limitation is that accuracy is less than acceptable. Conventional optical input power measurement solutions that utilize linear current-to-voltage conversion require calculation of a logarithmic function to convert voltage to optical power in units of dBm. Such a calculation or table look-up on an OLT will contribute additional error due to limited processing power and/or memory of the OLT. One further limitation is that RSSI measurement solutions that are built into a TIA or other data path devices have the effect of limiting which devices can be used in the data path.
Therefore, facilitating optical input power measurement in a manner that at least partially overcomes limitations associated with conventional approaches for facilitating optical input power measurement would be useful and advantageous.